GB2047802A

GB2047802A - Ic engine spark ignition chambers

Info

Publication number: GB2047802A
Application number: GB8012712A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-04-21
Filing date: 1980-04-17
Publication date: 1980-12-03
Also published as: DE2916285A1; US4513708A; GB2047802B; FR2454520A1; JPS6250646B2; IT8021446A0; JPS55142931A; US4442807A; DE2916285C2; IT1141457B; FR2454520B1

Description

1 GB 2 047 802 A 1 SPECIFICATION i Method and device for ignition of weak

fuel-air mixture The present invention relates to a method and device for ignition of weak fuel-air mixture.

Devices forthe ignition of weak mixtures are known, the purpose of such devices being to main- tain ignitability with a weak as possible combustion fuel-air mixture for an internal combustion engine. For example, fuel enrichment, which is achieved by a pronounced potential eddy formation in fresh mixture flowing into the ignition chamber, in the bound- ary zones of the turbulence is utilized to increase the ignitability of a relatively weak operational mixture, and also the ignition, improving the ignitability, within the wall boundary layer of this eddy current by a spark bridging over from an electrode to the ignition chamber wall. Furthermore, through regulation of the wall temperature to be of a high value, a good heating of the mixture to be ignited is achieved, which also increases the ignitability.

However, the known devices have the disadvan- tage thatthe ignition of fresh mixture in the ignition chamber takes place in the rear end of the ignition chamber so as to avoid undue thermal loading of the electrode of the spark plug. In this region, an increased residual gas component from the previous operating cycle has to be contended with and this reduces the ignitability. Known devices with transverse scavenging for removal of residual gas from the ignition chamber do not sufficiently improve the eddy formation and moreover lead to stronger cool- ing. It has also been proposed to locate the ignition electrode in a region where the fresh charge is weak in residual gas in orderto increase the ignitability of the mixture, but this has the disadvantage that the electrode is exposed to too strong a heat loading after ignition has taken place, which reduces the life of the electrode.

According to a first aspect of the present invention there is provided a method of igniting a weak fuel-air mixture in a combustion chamber of an internal combustion engine provided with an ignition chamber which communicates with the combustion chamber by way of a plurality of transfer ports and which receives ignition means associated with a wall of the ignition chamber, the method comprising the step of compressing mixture in the combustion chamberthereby to cause a portion of the mixture to be conducted through at least one of the transfer - ports to a region of the ignition chamber remote from the combustion chamber and another portion of the mixture to be so conducted into the ignition chamberthrough at least one other transfer port extending generally tangentially to said wall of the ignition chamber at a side of the chamber adjacent to the combustion chamber as to form a swirl along saidwall.

According to a second aspect of the present invention there is provided an ignition device for use in carrying out the method according to the first aspect, the device comprising means defining an ignition chamber, the chamber being substantially symmet- rical about an axis, ignition means comprising an electrode so arranged in association with a wall surface of the ignition chamber extending around said axis as to define with said surface an ignition spark disposed in a substantially central region of the ignition chamber with respect to its length in the direction of said axis, and at least one first and at least one second transfer port arranged to, in use of the device, connect the ignition chamber to a combus- tion chamber of an internal combustion engine, the or each first transfer port being so arranged as to, in use, conduct fuel-air mixture from the combustion chamber in direction generally towards a region of the ignition chamber remote from the combustion chamber and the or each second transfer port extending substantially tangentially to said wall surface to, in use, cause fuel-air mixture flowing through the or each second transfer portto form a swirl in the ignition chamber.

A method and a device exemplifying the invention have the advantage that each fresh mixture charge entering the ignition chamber is introduced in the form of two portions, one of which is brought by the tangentially extending port or ports into a rotating movement, which results in fuel enrichment in the wall boundary layer and consequent increase in the ignitability. Ignition can then take place in the wall boundary layer through a spark jumping over to the ignition chamber wall surface. The other portion of the charge is brought directly into the remote region or rear part of the ignition chamber and flows back from this region to obstruct the axial movement of the first-mentioned mixture portion. As a result, the dwell time of the introduced charge in the region of the electrode is increased. The part of the charge present in that region at the instant of ignition is enriched in fuel due to the previous rotation and is warmed up by the warm wall surface due to the longer dwell time. The reduced flow speed enhances the formation of the ignition spark. In particular, it is not necessary for the entire charge to be heated in order to achieve the desired ignitability. This increases the speed of heating with a given heat capacity of the ignition chamber wall surface. The ignition chamber itself can be kept small. In addition, the part of the fresh charge flowing in can advantageously serve for the cooling of the electrode or the component carrying the electrode.

Preferably one or more hollow spaces, which are filled with an evaporable medium serving for heat conduction (heat pipes), are arranged at least in the region of the electrode in parts of wall means which define said wall surface of the ignition chamber and adjoin cooled parts of the engine. As a result, a suffi- ciently high wall surface temperature in the ignition chamber is reached soon after starting the engine, yetthe temperature does not rise to such a level as to cause premature self-ignition of the mixture.

Advantageously, the ignition means comprises a heat-dissipating insulating body in which the electrode is embedded, the body projecting into the ignition chamber and surrounding the electrode up to a point close to the spark gap. As a result, the electrode is protected against undue heating.

Embodiments of the present invention will now be 2 more particularly described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is a sectional elevation of an ignition device according to first embodiment of the invention, the device having an ignition chamber with heat pipes in cylindrical walls thereof and axially and tangentially directed transfer ports in a nose of the device facing an engine combustion chamber; Fig. 2 is a cross section of the nose of the device of Fig. 1; Fig. 3 is a sectional elevation of part of an ignition device according to second embodiment of the invention, the device having a substantially frusto conical ignition chamber into which a conical insulat ing body carrying an ignition electrode projects 80 eccentrically; Fig. 4 is a sectional elevation of part of an ignition device according to a third embodiment of the inven tion, the device being a modification of that of Fig. 3 and having a cylindrical ignition chamber with an 85 enlarged region; Fig. 5 is a sectional elevation of part of an ignition device according to a fourth embodiment of the invention, the device having a cylindrical ignition chamber and a transfer port which extends through a wall of the ignition chamber from the part thereof projecting into the combustion chamber to the part remote from the combustion chamber; Fig. 6 is a cross-section of the device of Fig. 5; Fig. 7 is a sectional elevation of part of an ignition device according to a fifth embodiment of the invention, the device having a thermally insulated end wall provided exclusively with tangentially extending transfer ports; Fig. 8 is a sectional elevation of part of an ignition 100 device according to a sixth embodiment of the invention, the device having a frusto-conical ignition chamber and a transfer port leading to the rear part of the ignition chamber and containing a non-return valve.

Referring now to the drawings, in Fig. 1 there is shown a part of a combustion chamber wall 1 which bounds a main combustion chamber 3 of an internal combustion engine. Provided in this part of the combustion chamber wall is a stepped bore consist- 110 ing of a first bore section 4 at the end of the bore adjacent to the combustion chamber and a bore section 5 which adjoins the section 4, is of larger diameter, and is provided with an external thread 6. An insert 7, which is adapted in shape to the shape of the stepped bore and which contains an ignition chamber 8, is inserted into the stepped bore. The ignition chamber consits of a cylindrical first chamber part 10 extending substantially over the bore section 4, and a similar cylindrical rear chamber 120 part 9 adjoining the part 10 and disposed in the region of the bore section 5. The part 10 is closed off at the side of the combustion chamber 3 by a wall with an end face 12 which projects into the combustion chamber. Arranged in the part 10 of the ignition chamber are second transfer ports 13 extending tangentially to the chamber part 10 and a first transfer port 14 extending co-axially to the ignition chamber axis. The end face 12 is provided with a stub 16 which projects into the ignition chamber GB 2 047 802 A 2 beyond the entry openings of the parts 13 and thus seves as a guide forthe mixture quantities entering through these ports and favours the formation of an eddy.

An opening 18, through which projects a rotationally symmetrical insulating body 20 arranged coaxially of the ignition chamber, is provided in an end face 17 of the insert opposite to the end face 12. The insulating body 12 is part of an ignition device which essentially represents part of a modified spark plug. The insulating body is retained in a housing 22 and is in heat-conducting contact therewith. The housing 22 is threadedly engaged with the thread 6 and has a planar pressure face 23 for holding the insert 7 in the stepped bore. A mica plate 24 serving for heat insulation is arranged between the pressure face 23 and the end face 17 of the insert. In this manner, the insert 7 is located in the combustion chamber wall and the combustion chamber 3 is sealed off.

The insulating body 20 has a conical part 26 projecting into the ignition chamber to about the middle region of the part 10. An electrode 21 which serves for conducting an ignition voltage, is embedded in the insulating body. The electrode has a connecting portion 27 at the outer, prolonged part of the insulating body, and a portion which projects from the end of the part 26 of the insulating body into the proximity of a cylindrical wall 28 defining the chamber part 10 and which forms a spark gap 29 therewith. The gap 29 is disposed substantially in the wall boundary layer of the mixture current in that region of the ignition chamber.

An annular, liquid-filled heat pipe 31, which serves for regulation of heatflow out of the ignition chamber 8 to adjoining cooled spaces 32 in the cornbustion chamber wall 1, is arranged in the wall 28.

Fig. 2 shows, in cross-section, the lower part of the insert 7 which projects into the combustion chamber 3. The arrangement of the ports 13 as well as the position of the port 14 are evident from Fig. 2.

Each charge of fuel and air mixture introduced into the combustion chamber 3 during the suction stroke of the engine is forced during the subsequent compression stroke through the ports 13 and 14 into the ignition chamber 8. The mixture part flowing through the port 14 flows directly towards the conical part 26 of the insulating body 20, diverges at that point, and flows into the rear part 9 of the ignition chamber, where a reversal of the flow then takes place. At the same time, the other part of the mixture flows through the ports 13. Due to the angles of the ports 13, the introduced mixture is caused to rotate so as to provide a vortex which moves along the wail 28 and surrounds the mixture flow issuing from the port 14. The stub 16 promotes an orderly formation of the vortex. Due to the high rotational speed of the. weak mixture quantities, such quantities are enriched in fuel in the region nearthe wall. The enriched mixture is warmed up atthe wall 28, whereby its ignitability is further increased. The axial component of the vortex is, however, increasingly damped as the mixture quantity approaches the electrode 21, due to the influence of the quantity which has flowed in through the port 14 and is now flowing back from the end face 17. Finally, rotary i 3 GB 2 047 802 A 3 movement of the mixture quantity which has flowed in through the ports 13 only continues in the region of the ignition spark. This mixture, enriched by centrifugal force, remains in the region of the wall 28 controlled by the heat pipe 31.

The incorporated heat pipe 31 is able to prevent, in the cold state of the ignition chamber, heat transfer to the cooled combustion chamberwalls and also overheating of the ignition chamber wall in the case of the ignition chamber being heated above the temperature at which the heat pipe provides heat transference. An optimum highest temperature is thus maintained by the heat pipe. Heat pipes as such are known and operate on the principle that above a certain temperature the liquid in the heat pipe is vaporised, while the vapour condenses again at the cooler parts of the heat pipe. The condensate is returned to the evaporation point through a heat pipe insert which has a plurality of capillary gaps or openings.

For providing a temperature increase of certain parts of the wall 28, an insulation gap 33, which separates the heat pipe part of the insert from the adjoining cooled combustion chamber wall 1, can be provided atthe outer surface of the insert 7. Due to the build-up of heat in this region of the wall 28, it attains an increased temperature which is, however, controllable by the application of the heat pipe.

The ignition electrode 21 forms the spark gap 29 in about the middle part of the ignition chamber. The volume of the ignition chamber above the crosssectional plane at the level of the spark gap 29 is about twice as great as the volume below this plane. Only a short length of the electrode is exposed in the ignition chamber. The remaining length of the electrode is enclosed by the insulating body 20. Due to the conical construction of the part 26, an effective heat transfer from the electrode 21 to the housing 22, and from there to the cooled combustion chamber wall 1, is ensured. In this manner, the thermal loading of the electrode 21 can be kept very low. The insulating body at the same time serves for uniform distribution of the mixture quantity flowing in through the port 14 and this quantity on the one hand is warmed up by the insulating body and on the other hand cools this body during the inflow phase.

A desired volume division of a desired ratio of directly introduced mixture to the mixture brought into rotational movement can be achieved through the dimensioning of the cross-sections of the ports 13 and 14. Only the mixture brought into rotational movement serves forthe initial ignition. It is necessary forthis relatively small part to be heated up as much as possible only at the point at which the ignition spark jumps overto the wall. The remaining part of the charge introduced into the ignition chamber serves to give the entire mixture the energy content necessary for ignition in the main combustion chamber.

The ignition is also prompted by the fact that the sparkjumps over within the wall boundary layer in which the gas speed reduced to nothing and thus has a lower mean speed than the mixture in the adjoining regions of the ignition chamber. There is therefore no danger of the ignition spark decaying, by reason of too high a mixture movement, before it effects ignition of the mixture.

The ignition chamber orthe insert, and particularly the diameter of the chamber part 10 can be small in size, as the necessary volume is provided by the enlarged rear part 9 of the ignition chamber. Due to the relatively small diameter of the chamber part 10, the insert can be accommodated more easily in the combustion chamber wall 1. The space availability in modern internal combustion engines is very limited, as the inlet and outlet valves require the greatest part of the surface. According to the position of the insert, the arrangement of the ports 13 is appropri- ately adapted so that the flame issuing into the combustion chamber after ignition of the mixture optimally ignites the charge component in the combustion chamber. The insert 7 is easily exchangeable and, due to the insulation provided by the insulation gap 33 and the mica plate 24, enables preheating of the introduced mixture even at low loads.

Fig. 3 shows a modified form of the embodiment of Fig. 1. In this case there is provided an ignition chamber insert 37, which is retained by a housing 38 of an ignition means in a stepped bore 39. The insert 37 contains, in contrast to the embodiment of Fig. 1, a frusto-conical ignition chamber 40. The outer shape of the insert 37 is also frusto-conical, the tapering part of which projects into the main combustion chamber 3. Provided at an end face 41 of the insert is a central first transfer port 42, which is directed towards an oppositely disposed end face 43 forming the base of the insert. Extending laterally of and perpendicularly to the axis of the insert are two second transfer ports 44, which open tangentially into the ignition chamber 40 and impart a rotational movement to mixture flowing through the ports. As in the first embodiment, the mixture issuing fiorn the ports 44 circulates around the mixture jet issuing from the port 42.

Provided eccentrically on the end face 43 is an opening 45, which is surrounded by a conical sleeve 46 tapering inwardly into the interior of the ignition chamber 40. Projecting through this opening 45 is a conically formed nose 48 of an insulating body 49, which surrounds a straight centre electrode 50, which issues at the end of the nose 48. The insulating body, which preferably consists of spark plug type ceramic material, is inserted into the housing 38 and is in heat-conducting contact therewith. The type of ceramic body insert with electrode provided in a conventional spark plug can be used. The electrode 50 extends through the insulating body up to a conical wall 51 of the ingnition chamber and defines with the wall a spark gap 52. The wall 51 in this region has an annular bead 53. The conical wall 51 contains a heat pipe 54 analogous to the heat pipe of 31 of Fig. 1. The heat pipe 54 can, of course, consist of several individual pipes.

This embodiment has the advantage that the ceramic of a customary spark plug can be employed in the ignition device. The sleeve 46 which protects the lower foot part of the nose 48 against heating is provided in advantageous manner. The cone angle of the sleeve 46 is equal to the cone angle of the nose 4 GB 2 047 802 A 4 48. An air gap 47, closed off towards the ignition chamber, is present between sleeve 46 and nose 48.

The axis of the first transfer port 42 is not quite coincident with the axis of the insert 37, but is so arranged that the central mixture jet issuing from the port 42 is directed into the centre of the rear part 55 of the ignition chamber 40. Due to the conical enlargement of the ignition chamber 40 in direction away from the inflow point of the ports 44, after an initial rapid rotational movement of the tangentially introduced mixture component this movement slows down and is further braked by the mixture flowing back from the rear part 55 of the ignition chamber. With this arrangement, the mixture com ponent flowing in directly is greaterthan the rotating mixture component issuing from the ports 44. This is heated up intensively atthe conically shaped wall 51, the temperature of which is regulated bythe heat pipe 44. A part of the conically shaped wall projects into the main combustion chamber 3 so thattransfer of heat from this wall part to a cooled wall 56 of the combustion chamber 3 is reduced. The encircling bead 53 effects an intensive flow around the wall in the region of the ignition point, whereby the wall in this region has a relatively high temperature. 90 Compaed with the advantages mentioned in con nection with the first embodiment, the device of Fig.

3 has the advantage of an even smaller space requirementfor the part of the ignition chamber pro jecting into the main combustion chamber. Only a very small part, intended for initial ignition, of the introduced charge is heated intensively and enriched with fuel in the wall region by rotation, so thatthe mixture may reach the state of optimum ingnitability in a short time.

The embodiment according to Fig. 4, like the embodiment according to Fig. 3, has an eccentrically inserted insulating body 49, which is retained in a housing 38 threaded into the stepped bore 39 (c.f.

Fig. 3). The housing 38 locates an ignition chamber insert 59 in the stepped bore 39. The insert 59 is constructed similarly to the insert 7 of the device of Fig. 1 and encloses an ignition chamber which con sists of a first cylindrical part 60 of small diameter and an adjoining rear cylindrical part 61. The part of the insert 59 containing the chamber part 60 has an end face 62 and a cylindrical wall portion projecting into the combustion chamber 3. The end face 62, as in the embodiment of Fig. 1, has a central first trans fer port 63, the axis of which is slightly offset relative to the axis of symmetry of the insert 59. In the region of the port 63, the end face 62 is provided on its side facing into the ignition chamber with a stub 64, which, similarly to the embodiment of Fig. 1, serves forthe guidance of mixture quantities flowing through second transfer ports 65 into the first chamber part 60. The ports 65 are arranged in a cylindrical wall 66 bounding the chamber part 60 to extend tangentially to the ignition chamber and sub stantially radially, the ports being disposed atthe end of the wall 66 directly adjoining the end face 62.

A heat pipe 67 is provided in the wall 66, as in the embodiment of Fig. 1, and extends overthe entire length of the wall 66.

The rear chamber part 61 is bounded by an end face 68, which has an opening 69 disposed eccentri- cally of the ignition chamber axis. The opening is surrounded by a conically narrowing sleeve 70, which projects into the rear chamber part 61 and serves for the reception of the nose 48 of the insulating body 49. This insulating body is of similar construction to the one in the embodiment of Fig. 3 and has a straight centre electrode 50, which defines a spark gap 52 with the wall 66. The spark gap is disposed atthe end of the wall 66 opposite the end face 62. The wall 66, in the region of the spark gap 52, projects freely into the rear chamber part 61 so as to define a recess 71 which extends over about half the external circumference of the wall 66.

In this embodiment, a part of the fresh mixture charge is introduced through the port 63 to provide a mixture jet which is directed towards the centre of the rear chamber part 61. Another part of the fresh mixture charge flows through the ports 65 and is brought into rotation so asto provide a vortex as described in connection with the embodiment of Fig. 1. The mixture is heated intensively by the heat pipe 67 provided in the chamber wall but without being overheated. This embodiment affores a higher heat transfer rate from the cylindrical wall in the region of the spark gap 52, as the wall in this region freely projects into the rear chamber part 61. This, in the zone where there is a longer duration of the mixture, there are lower heat losses and consequently an increase in the degree of heating of the mixture. This arrangement is very compact, with an ignition chamber insert part of relatively small diameter projecting into the main combustion chamber. Furthermore, the possibility is afforded of using the ceramic element of a conventional spark plug as part of the ignition means. The ceramic element can extend up to the ignition point between the electrode and ignition chamber wall, so as to minimise the thermal loading of the ignition electrode by good heat trans- fer from the element. The heating of the insulating body is further reduced by provision of the sleeve 70, which conforms to the cone angle of the nose 58 and covers a substantial part of the nose so as to protect it against heat absorption, whereby the ceramic of the insulating body only has to conduct away the heat arising at the nose in the region of the electrode.

The embodiment according to Fig. 5 is constructed similarly to the embodiment according to Fig. 1. In this case, there is provided on the end face 17, in the region of the opening 18, a sleeve 73 which conically tapers into the interior of the rear chamber part 9 and covers the base of the nose 26 of the insulating body 20 so as to protect it against heat induction. In addi- tion, one ortwo furthertransfer ports 74 are provided in the cylindrical wall 28'and extend parallel to the axis of symmetry of the ingnition chamber insert 7'to open freely into the rear chamber part 9. At their other ends, the ports 74 have openings 75 com- municating with the main combustion chamber 3. As is to be inferred from the cross-section of Fig. 6, the heat pipe 31'then consists of, for example, two halves which are separated from each other by the two ports 74.

In this embodiment, during the compression 1 R stroke of the engine, a part of a fresh charge is forced through the ports 74 directly into the rear chamber part 9 and from there flows back towards the first chamber part 10. At the same time, another part of the charge part is so forced through the ports 13 at the end of the first chamber part 10 at the side of the combustion chamber as to be set into rotational movement. The mutually opposite axial movements of the two mixture parts cancel each other in the region of the electrode 21, so that these mixture parts have an increased dwell time in this region, particularly the rotating mixture part. Ignition takes place in the boundary layer region, in which the mixture is enriched in fuel due to the rotation, has a low mean speed of flow, and is optimally heated. The boundary between the rotating mixture part and the mixture part flowing back from the rear chamber part 9 can be fixed by dimensioning the crosssections of the ports so that ignition always takes place in the region where the mixture is enriched with fuel by the rotational movement and almost free of residual gases from the preceding combustion process, so that optimum ignition conditions result. In this embodiment, the first transfer port 14 can be dispensed with.

The embodiment according to Fig. 7 shows a variant of the embodiment according to Fig. 5, the central port 18-arranged in the end face 12 in the Fig. 1 embodiment-being dispensed with. The end face 12' in the embodiment of Fig. 7 is constructed as a bowl-shaped insert with tangentially extending ports 13'. The end face 12' in that case is the only part of the ignition chanber insert which projects into the main combustion chamber. The end face 12'is inserted into the bore of the cylindrical wall 28', so thatthe wall thickness between the inner surface of the end face 12'and the heat pipe 31' in the cylindrical wall 28'is increased. The end face 12'is, as a consequence, more strongly heated, so that the fresh mixture is rapidly warmed up immediately on 105 entry through the ports 31'.

The embodiment according to Fig. 8 is a variant of the embodiment according to Fig. 3. The ignition chamber insert 77 has the shape of a conical frus- tum, the nose of which projects into the main combustion chamber 3. Departing from the embodiment of Fig. 3, there is provided, in place of the first transfer port 42 on the end face 41 of the ignition chamber insert, a first transfer port 78 which extends in a con- ical wall 79 at least on the inside and opens directly into a rear chamber part 80.At the side of the combustion chamber, a first transfer port 78 has an opening 81, whereby the rear chamber part, which is opposite an end face 82 projecting into the combus- tion chamber, is connected through the port 78 with the combustion chamber. Immediately adjoining the end face 82, the ignition chamber insert has second transfer ports 84 extending tangentially to a frustoconical ignition chamber 83 enclosed by the insert 77. An end face 85 opposite the end face 82 adjoins a housing 86, which receives an insulating body 87 which, like the insulating body 20 of the device of Fig. 1, surrounds an electrode 88. The electrode 88 projects out of a conical nose 89 of the body 20 towards the wall 79 and defines a spark gap 90 with GB 2 047 802 A 5 the wall. The conditions governing the position of the spark gap with respectto the axial length of the ignition chamber insert 77 or ingniton chamber 83 are the same as those described in connection with the preceding embodiments. The insert 77 is retained in a bore 91 in the combustion chamber wall 1 by the threaded-in housing 86, with care being taken to obtain a tight closure of the combustion chamber. This can advantageously be effected by a conical sealing surface 92 at the outer circumference of the insert 77 in the region of the bore 91.

The insulating body 87 in departure from the embodiment according to Fig. 3, is inserted coaxially with the insert 77 and has a cylindrical part 93 adjoining the base of a conial nose 89. The part 93 extends through a central opening 94 in the end face 85 and is surrounded by a cylindrical sleeve 95 extending into the ignition chamber. This sleeve 95 serves for the screening of the insulating body against the heat arising in the ignition chamber 83. The shape-enlarging in diameter from the ignition electrode 88-of the insulating body promotes heat transfer from the surface of the insulating body projecting into the ignition chamber 83. Analogously to the embodiment according to Fig. 5, a part of a fresh charge flows through the port 78 directly into the rear chamber part 80 during the compression stroke of the engine, while at the same time another part of the charge flows through the ports 84 into the igni- tion chamber 83. This latter part of the charge is, as already described, set into rotational movement, the rotational component of which gradually slows down by reason of the enlarging diameter of the ignition chamber and the axial component of which is similarly slowed down by the mixture part flowing back from the rear chamber part 80.

The first transfer port 78 has a non-return valve 96 in the form of a flutter valve, which opens in the direction of flow into the ignition chamber and closes in the reverse direction. Flutter valves are generally known and a suitably adapted flutter valve can be used for the non-return valve. This entails the advantage that, after ignition of the heated mixture, the flame only issues through the ports 84 into the combustion chamber, so that the entire charge of the ignition chamber can be utilised optimally for ignition of the mixture in the main combustion chamber 3. The ignition duration can in this manner be prolonged in relation to the filling duration of the igni- tion chamber 83. This embodiment with the centrally inserted insulating body 87 also affords the advantage that the mixture issuing from the ports 84 can be formed into a vortex without disturbance, as the volume of the ingition chamber has a rotationally symmetrical shape. Advantageously, the cone angle of the nose 89 corresponds to that of the wall 79.

The principle employed in the embodiment described above makes it feasible to use relatively small ignition chamber inserts with a small axial

Claims

length. Due to the slowing-down of the axial movement component of the rotating mixture in the ignition chamber, the heat exchange surface can be kept small, which favours this mode of construction. CLAIMS

1. A method of igniting a weak fuel-air mixture in 6 a combustion chamber of an internal combustion engine provided with an ignition chamber which communicates with the combustion chamber by way of a plurality of transfer ports and which receives ignition means associated with a wall of the 70 ignition chamber, the method comprising the step of compressing mixture in the combustion chamber thereby to cause a portion of the mixture to be conducted through at least one of the transfer ports to a region of the ignition chamber remote from the combustion chamber and another portion of the mixture to be so conducted into the ignition chamber through at least one other transfer port extending generally tangentially to said wall of the ignition chamber at a side of the chamber adjacent to the combustion chamber as to form a swirl along said wall.

2. A method of igniting a weak fuel-air mixture in a combustion chamber of an internal combustion engine, the method being substantially as hereinbefore described with reference to any one of Figs. 1, 3, 4,5,7 and 8.

3. An ignition device for use in carrying out the method as claim,-d in claim 1, the device comprising means defining an ignition chamber, the chamber being substantially symmetrical about an axis, ignition means comprising an electrode so arranged in association with a wall surface of the ignition chamber extending around said axis as to define with said surface an ignition spark gap disposed in a substantially central region of the ignition chamber with respect to its length in the direction of said axis, and at least one first and at least one second transfer port arranged to, in use of the device, connect the ignition chamberto a combustion chamber of an internal combustion engine, the or each first transfer port being so arranged as to, in use, conduct fuel-air mixture from the combustion chamber in direction generally towards a region of the ignition chamber remote from the combustion chamber and the or each second transfer port extending substantially tangentially to said wall surface to, in use, cause fuel-air mixture flowing through the or each second transfer port to form a swirl in the ignition chamber.

4. A device as claimed in claim 2, wherein the transfer port extend through wall means extending, in use of the device, between the ignition and combustion chambers and comprise at least a first transfer port directed towards said remote region of the ignition chamber and a second transfer port extending substantially tangentially to said wall surface with respectto the axis of said first transfer port.

5. A device as claimed in claim 2, wherein at least one of the transfer ports extends through wall means extending, in use of the device, between the ignition and combustion chambers and the transfer ports comprise at least a first transfer port connected at one end thereof with said remote region of the ignition chamber and a second transfer port extend- ing substantially tagentially to said wall surface with respect to said axis of the ignition chamber.

6. Adevice asclaimed in anyone of claims3to 5, wherein the spark gap is disposed in a plane which extends perpendicularly to said axis of the ignition chamber and which divides the volume of the igni- GB 2 047 802 A 6 tion chamber into a portion adjacentto and a portion remote from the combustion chamber, the former portion being at most equal in volume to the latter portion.

7. Adevice as claimed in anyone of claims3to 6, further comprising means defining at least one heat cc.-.trol chamber, which is filled with an evaporable medium and which is so arranged in wall means defining said wall surface as to extend at least in the region of the electrode.

8. A device as claimed in claim 7, wherein the or each heat control chamber is formed as a heat pipe.

9. Adevice asclaimed in anyone of claims3to 8, wherein the ignition chamber is provided in an insert body adapted for mounting in an opening in a wall of the engine defining such combustion chamber.

10. A device as claimed in anyone of claims3to 9, the ignition means further comprising an electrically insulating body which is arranged to project in part into the ignition chamber from an end thereof remote from the combustion chamber and which surrounds the electrode up to a point immediately adjacent to the spark gap.

11. A device as claimed in claim 10, wherein the part of the insulating body projecting into the ignition chamber is substantially conical in shape.

12. A device as claimed in either claim 10 or claim 11, the ignition means further comprising an externally threaded housing retaining the insulating body.

13. A device a claimed in claim 12 when appended to claim 9, wherein the insert body is adapted to be retained in said opening by the insulating body.

14. A device as claimed in anyone of claims 9to 11, wherein the ignition chamber is defined at a side thereof remote from the combustion chamber by a wall provided with an opening forthe part of the insulating body projecting into the ignition chamber and with a substantially conical sleeve element extending around said part.

15. A device as claimed in claim 14, wherein the insulating body is elongate in shape and the electrode extends substantially along the longitudinal axis of the body, the body being so arranged that its longitudinal axis is displaced relative to said axis of the ignition chamber.

16. A device as claimed in anyone of claims 3to 15, wherein the breadth of the ignition chamber transversely of said axis thereof is greater in said remote region than in the region of the ignition chamber closest to the combustion chamber.

17. A device as claimed in claim 16, wherein the ignition chamber is substantially conical in shape. 120

18. A device as claimed in claim 17, wherein the ignition chamber is frustoconical in shape.

19. A device as claimed in either claim 17 or claim 18 when appended to claim 9, wherein the cone angle of the ignition chamber substantially cor- responds to that of said projecting part of the insulating body.

20. A device as claimed in anyone of claims 3to 19, wherein said wall surface defines a rib-like projection in the region of the spark gap.

21. A device as claimed in claim 5, comprising a 1 7 GB 2 047 802 A 7 non-return valve arranged in said firsttransfer port to permitthe flow of mixture therethrough only in direction towards said remote region of the ignition chamber.

22. A device as claimed in anyone of claims3to 21, wherein the breadth of the ignition chamber transversely of said axis thereof is greater in said remote region than in the region of the ignition chamber closest to the combustion chamber and wherein said wall surface is in part defined by a wall which in the region of the electrode extends into and terminates in said remote region and which incorporates heat control means.

23. A device as claimed in anyone of claims3to 22, wherein the ignition chamber is provided in an insert body adapted for mounting in an opening in a wall of the engine defining such combustion chamber and wherein the transfer ports comprise a first transfer port extending through wall means, which defines said wall surface and an exterior wall surface engageable with a surface defining that opening.

24. A device as claimed in claim 8, wherein said wall means further defines an exteriorwall surface which includes a thermal insulation recess extending over at least part of the length of the heat pipe in the direction of said axis of the ignition chamber.

25. A device as claimed in claim 3 and substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.

26. A device as claimed in claim 3 and substantially as hereinbefore described with reference to Fig. 3 of the accompanying drawings.

27. A device as claimed in claim 3 and substan- tially as hereinbefore described with reference to Fig. 4 of the accompanying drawings.

28. A device as claimed in claim 3 and substantially as hereinbefore described with reference to Figs. 5 and 6 of the accompanying drawings.

29. A device as claimed in claim 3 and substantially as hereinbefore described with reference to Fig. 7 of the accompanying drawings.

30. A device as claimed in claim 3 and substantially as hereinbefore described with reference to Fig. 8 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by The Tweeddale Press Ltd., Berwick-upon-Tweed, 1980. Published at the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.